1. Field of the Invention
The invention is related to a wind power generator, especially one that can control output power.
2. Description of the Prior Art
A wind power generator uses turbine blades to convert the wind energy into the mechanical energy, and then uses the power generator to convert the mechanical energy into the electric energy output. Thus, a common practice is to maximize the energy output before reaching the rated power. The wind power generator should always face the wind in the right direction. On the other hand, if the yaw direction for the wind power generator deviates from the wind direction by a large angle, the wind energy utilization efficiency will be low. This also means that at the same wind speed the wind power generator will have a lower output power. The control of direction for the wind power generator can be divided into active mode and passive mode. The active mode uses motor to change the direction for the wind power generator, while the passive mode uses tail wing to keep wind power generator to face the wind. The invention aims at the passive mode for improvement.
The passive direction control for wind power generator is as shown in FIG. 1A. The wind power generator 10′ has a rigid tail rod 12′ and a tail wing 14′. The center of rotation 101′ for the wind power generator 10′ is located at the central line for the wind power generator. When the wind power generator 10′ is facing the wind direction 2′, the turbine 103′ for the wind power generator 10′ only produces net axial force 105′ that passes the central line, so the net torque with respect to the yaw center 101′ for the wind power generator 10′ is zero and the wind power generator 10′ keeps facing the wind direction 2′. Besides, as shown in FIG. 1B, when the wind direction 2′ is changed and the wind direction 2′ and the wind power generator 10′ form an angle 107′, the turbine 103′ for the wind power generator 10′ produces lateral force (FBx) 109′ as well as axial force (FBy) 105′. The tail wing 14′ for the wind power generator 10′ also produces tail wing force (Ftail) 108′. At this moment, if the net torque relative to the yaw center for the wind power generator meets the following equation:Ftailc>FBxb+Mbearing The wind power generator 10′ will return from the status in FIG. 1B to the status in FIG. 1A. The Mbearing is the frictional torque for the bearing relative to the yaw center for the wind power generator 10′.
The above is the layout for a common wind power generator 10′ that uses tail wing 14′ to change direction. The yaw center 101′ for a wind power generator 10′ is located at the central line for the wind power generator 10′. The tail rod 12′ is made of rigid material. The function of the tail wing 14′ is only to control the wind power generator 10′ to face the wind direction 2′. At this moment, as shown in FIG. 2A, if the yaw center 101′ for the wind power generator 10′ is shifted from the central line (distance a), when the wind power generator 10′ is facing the wind direction 2′, the turbine blades 103′ for the wind power generator 10′ will produce axial force (FBy) 105′. If the net moment is larger than the static friction (Mbearing) of the bearing about the yaw center 101′, as shown in the following equation:FBya>Mbearing 
The wind power generator 10′ will deviate from the wind direction 2′ until the forces are in balance, as shown in FIG. 2B. The net moment about the yaw center 101′ for the wind power generator 10′ is shown in the following equation:FBya+FBxb=Ftailc+Mbearing 
Consequently, the wind power generator 10′ and the wind direction 2′ will form an angle 107′. As the wind speed increases, the axial force 105′, the lateral force 109′ as well as the tail wing force 108′ will increase simultaneously. As the result, the angle 107′ will remain unchanged or only increase a little bit. Therefore, if the wind power generator 10′ uses combination of yaw center 101′ shifting and rigid tail rod 12′, the wind power generator 10′ will produce an angle 107′ as the wind speed exceeds a certain value. However, this angle will not increase with wind speed. To solve the above issue, the invention utilizes a bendable elastic tail rod to control the power output.